Transparency doesn't work in building Qt from sources

[AspiringEngineer]

Hi,

I've encountered a problem in building a simple application using Qt 4.8.4 (built statically) and Linux Mint 14.



#include <QApplication>
#include <QLabel>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);

QLabel label("label");
label.setAttribute(Qt::WA_TranslucentBackground);
label.setFixedSize(400,400);
label.show();

return a.exec();
}

In my linux distribution I've enabled compositing and I've installed Qt Creator and the previous version of Qt libraries (4.8.3) from the repositories.
Using this version I don't have any problem with transparency, the label is shown as expected, but if I want to build statically my application using the 4.8.4 version, the background color is black.

I've tried to change the style using QApplication::setStyle(...) or using another Qt libraries version (4.8.2) built statically, but I was not able to solve the problem.
If anybody has any idea, please help me.
Thanks in advance